Pierella Karlusich Juan José, Bowler Chris, Biswas Haimanti
Institut de Biologie de l'ENS, Département de Biologie, École Normale Supérieure, CNRS, INSERM, Université PSL, Paris, France.
CNRS Research Federation for the study of Global Ocean Systems Ecology and Evolution, FR2022/Tara Oceans GOSEE, Paris, France.
Front Plant Sci. 2021 Apr 30;12:657821. doi: 10.3389/fpls.2021.657821. eCollection 2021.
Marine diatoms, the most successful photoautotrophs in the ocean, efficiently sequester a significant part of atmospheric CO to the ocean interior through their participation in the biological carbon pump. However, it is poorly understood how marine diatoms fix such a considerable amount of CO, which is vital information toward modeling their response to future CO levels. The Oceans expeditions generated molecular data coupled with biogeochemical measurements across the main ocean regions, and thus provides a framework to compare diatom genetic and transcriptional flexibility under natural CO variability. The current study investigates the interlink between the environmental variability of CO and other physicochemical parameters with the gene and transcript copy numbers of five key enzymes of diatom CO concentration mechanisms (CCMs): Rubisco activase and carbonic anhydrase (CA) as part of the physical pathway, together with phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase, and malic enzyme as part of the potential C4 biochemical pathway. Toward this aim, we mined >200 metagenomes and >220 metatranscriptomes generated from samples of the surface layer of 66 globally distributed sampling sites and corresponding to the four main size fractions in which diatoms can be found: 0.8-5 μm, 5-20 μm, 20-180 μm, and 180-2,000 μm. Our analyses revealed that the transcripts for the enzymes of the putative C4 biochemical CCM did not in general display co-occurring profiles. The transcripts for CAs were the most abundant, with an order of magnitude higher values than the other enzymes, thus implying the importance of physical CCMs in diatom natural communities. Among the different classes of this enzyme, the most prevalent was the recently characterized iota class. Consequently, very little information is available from natural diatom assemblages about the distribution of this class. Biogeographic distributions for all the enzymes show different abundance hotspots according to the size fraction, pointing to the influence of cell size and aggregation in CCMs. Environmental correlations showed a complex pattern of responses to CO levels, total phytoplankton biomass, temperature, and nutrient concentrations. In conclusion, we propose that biophysical CCMs are prevalent in natural diatom communities.
海洋硅藻是海洋中最成功的光合自养生物，它们通过参与生物碳泵，有效地将大气中的一部分二氧化碳隔离到海洋内部。然而，人们对海洋硅藻如何固定如此大量的二氧化碳知之甚少，而这对于模拟它们对未来二氧化碳水平的反应至关重要。海洋考察在主要海洋区域生成了分子数据并结合了生物地球化学测量，从而提供了一个框架，用于比较自然二氧化碳变化下硅藻的遗传和转录灵活性。本研究调查了二氧化碳的环境变异性与其他物理化学参数之间的相互联系，以及硅藻二氧化碳浓缩机制（CCMs）的五种关键酶的基因和转录本拷贝数：作为物理途径一部分的核酮糖-1,5-二磷酸羧化酶激活酶和碳酸酐酶（CA），以及作为潜在C4生化途径一部分的磷酸烯醇式丙酮酸羧化酶、磷酸烯醇式丙酮酸羧激酶和苹果酸酶。为了实现这一目标，我们挖掘了从全球66个分布采样点表层样本中生成的200多个宏基因组和220多个宏转录组，这些样本对应于可以发现硅藻的四个主要大小分级：0.8-5μm、5-20μm、20-180μm和180-2000μm。我们的分析表明，假定的C4生化CCM酶的转录本一般不显示共现模式。CA的转录本最为丰富，其值比其他酶高一个数量级，这意味着物理CCMs在硅藻自然群落中的重要性。在该酶的不同类别中，最普遍的是最近鉴定的iota类。因此，关于这一类别的分布，自然硅藻组合提供的信息非常少。所有酶的生物地理分布根据大小分级显示出不同的丰度热点，这表明细胞大小和聚集对CCMs有影响。环境相关性显示了对二氧化碳水平、总浮游植物生物量、温度和营养浓度的复杂反应模式。总之，我们认为生物物理CCMs在自然硅藻群落中普遍存在。
